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Updated: Aug 8, 2026

Characterization of Membrane Transporters by Heterologous Expression in E. coli and Production of Membrane Vesicles
Published on: December 31, 2019
Transport Properties of the Tomato Fruit Tonoplast : II. Citrate Transport
N Oleski1, P Mahdavi, A B Bennett
1Mann Laboratory, Department of Vegetable Crops, University of California, Davis, California 95616.
Abstract:
Citrate transport across the membrane of tomato fruit tonoplast vesicles was investigated. In the tonoplast vesicles, [(14)C]methylamine uptake was stimulated 10-fold by MgATP and strongly inhibited by NO(3) (-). Under identical experimental conditions, [(14)C]citrate uptake was inhibited by 5 millimolar free Mg(2+), and this inhibition was reversed in the presence of ATP, presumably by ATP chelation of free Mg(2+). No evidence was obtained in support of energy-linked ATP stimulation of citrate uptake. Citrate uptake showed saturation kinetics, and was inhibited by 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid and by other organic acids. The pH-dependence of uptake suggested that citrate(3-) was the transported species. Our results indicate that citrate transport across the tomato fruit tonoplast occurs by facilitated diffusion of citrate(3-). The carrier shares some features in common with anion channels in that it is relatively nonspecific for organic acids and is inhibitable by 4,4'-diisothyocyano-2,2'-stilbenedisulfonic acid.
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